The use of metal soap aqueous dispersions as additives useful for many purposes, such as: improving the flowability of polymers and especially of polyvinyl chloride, as lubricant for paper coating, in SBR as waterproofing agent, as thickeners, etc. This appears from a large number of patents published in the last twenty years on this subject. Some of these references are describing the improvement obtained in the flowability of polyvinyl chloride powder, thus preventing a decrease in its bulk density due to a static build-up on suspension polymers of vinyl chloride.
Metal salts of carboxylic acids containing between 8 to 28 carbon atoms are known as soaps. The characteristic feature of metal soap aqueous dispersions is the presence of a water insoluble carboxylate salt.
According to Japanese Patent Number 59' 51,236 (mentioned in C.A.101, 40223), metal soaps aqueous dispersions were obtained by homogenizing powdered calcium stearate, oleate or palmitate with water, in the presence of surfactants selected from ethoxylated lauryl alcohol and sodium dodecyl sulfate.
According to another Japanese Patent Application 76 34904 (mentioned in C.A. 85,23038), slurries of metal soaps having high concentrations of active constituents are prepared by the reaction of alkali salts of fatty acid with water-soluble metal salts at a temperature of between 65.degree. to 105.degree. C. in the presence of a surfactant. An example as given in the abstract, is calcium stearate slurry, prepared from sodium stearate, a solution of calcium chloride and polyoxyethylene nonylphenyl ether.
In the German (East) Patent Number 106,629 (mentioned in C.A. 82,74823), metal soap dispersions are prepared from stearin, water, an ethylene oxide-alkylphenol condensate, acetic acid and calcium hydroxide, or zinc oxide at a temperature of between 85.degree. to 90.degree. C. As an advantage of the method it is mentioned that the final product contained less than 0.17% of free fatty acid. However, the main disadvantage of the methods described in the above two patents, is the fact that water soluble salts, sodium chloride--in the first one--and calcium acetate--in the second one--which resulted as by-products in the respective reactions involved, remain in the final dispersions. This is a significant disadvantage,since these impurities are detracting the electrical properties of the resin.
An interesting method for obtaining a homogenized aqueous dispersion of calcium stearate, zinc stearate and calcium oleate, is described in the Japanese Patent Application Number 82'77642 (mentioned in C.A. 97, 91751). The main feature of the method for obtaining the dispersion is that the reagents--free acids and calcium hydroxide,--in the presence of an anionic surfactant containing a lyophilic alkyl phenol, or higher alcohol residue, are thoroughly mixed by a mechanical device under high pressure.
A similar method is also described in a very recent Japanese Kokai Application 02'191,539 (mentioned in C.A. 114, 8456). As realized, the use of pressure which requires special equipment, mentioned to impart a good storage stability, is a significant inconveniency of these methods.
One of the main disadvantage of all the above methods, is the fact that a non-ionic surfactant is incorporated and it remains in the final product causing soiling of the dispersion of the metal soap. Furthermore, it is well-known that the emulsifying agents are generally reducing the thermal and storage stability of resins and particularly of polyvinyl chloride.
The above brief review of the prior art, illustrates the problems which exist to-day for preparing metal soap aqueous dispersions, without detracting by their incorporation in the polymers processing, the properties of the final products obtained.
It is an object of the present invention to provide a novel method for the manufacture of metal soap aqueous dispersions. It is another object of the present invention, to provide a novel method for the manufacture of metal soap aqueous dispersions, without adding a non-ionic surfactant. It is a further object of the present invention, to provide a novel method for the manufacture of metal soap aqueous dispersions, wherein a ionic surfactant is formed in-situ and does not remain in the final product. It is yet another object of the present invention, to provide a method for obtaining metal soap aqueous dispersion, which are not containing any foreign impurity from the starting reagents.